Method of photographing printing forms



Sept. 2,1952 6. MORRISON METHOD OF PHOTOGRAPHING PRINTING FORMS 2 SHEETS--SHEET 1 Filed Dec. 2, 1948 PLANO -PELIEF S (JR/Ac l" Ja g/gyfi /fw/zwz AM, Go -val dam Sept. 2, 1952 G. MORRISCQJN 2,609,293

METHOD OF PHOTOGRAPHING PRINTING FORMS Filed Dec. 2, 1948 2 SHEETS-SHEET 2 0%! ammo.

i atented Sept. 2, 1 952 UNITED STATES OFFICE, Y

METHOD F PHoToGfilgPHlN G BRINTING- R George L. Morrison, Evanston, 2111.

Application December 2, 1948 ;Se :ial No. 63,037

5'Claims.

'1 The present 'inventio'nrrelates broadly to the art of printin and s part ula ly ncerned with apparatus and methods for photographing printing surfaces of either the raised or the intaglio type. In certainlof its aspects, the present.

invention is related .to, and is an improvement upon, theinvention of my prior application, SEN. 20,214, which was filed on Apri1 10, l948,.

Aspointedcut in my said prior application, it is the practice inthe everydayjproduction of certain typesof gravureand, other photo-mechanical relief; surfaces to be reproduced, this formbeing then" inked, andan impression on paper made therefrom} Finally, the inked impression has been photographed, and the resulting print or transparency usedin ,the production of ,the gravure or other photo-mechanical printing surface.

Despite the loss of clarity which results ,from the inking and printing operations, this process has beemextensively usedjortheleason that the direct photographingof printing storms has been considered impractical, if notin fact. impossible. In myprior applicationilhave disclosed aimethod of V pteparing v printing forms (which may include typeI andgtype-slugs of .various kinds and varieties as well as printingplatesmade of .various metals) so asto obtain; by a directphotographic process, a: photographic negative orpositive whichcan be used in the production of gravure and other photomechanical printingsurfaces of any of the known types.

In thepracticeof the inventiondisclosed in my said prior application, the surfaces of the printingiorm are treated in such manner that the plane-relief areas to be photographedhave generally uniform light reflectance propertiesand are sharply outlined by relatively non reflecting areas. This makes possible ,the direct photo.- graphingofprinting forms as above described.

The principal object of thepresentinvention is to provide an improved apparatus and-procedure foriilluminating and for photographing printing forms ,andlike-copy material and.mor e particularly, to provide an improved apparatus and pro cedure for illuminatingand for photographing,

the planoerelief surfaces of letter-press printing, forms so asto create ashadow area vwhichoutlines and sharply defines such surfaces fromtheir background. Other objects include the provisionpft a-novelv method and. apparatus for photographing. raised, or intaglio printing surfaces, in accordance with the above-stated principal object', by the use of conventional photographic methods and material t r u e p intsditi hfi parencies having adequate density andjccntrastz ,for p o-mec ani pu po es w hnii ith ne d lo al o eneral ntens fica i 9f th ima e an enerally th pro is on imnmr .apnma: hi and m t od ior oht nine ph t r phic prints :Qr t anspa enc of th ar u Pi n relief, prin i s rfac L Jiil11YQD 23i i fliin printing ,forms.

The inv ntion is :based n t di ove ha h density, shar l defin photqa anh m a es .o un orm contrast ca h obtain d l em type and li e p in ing sur ace b the 1 Q an i a ynhnt eensrave f c m a provided t a e i luminatio .1 .6 surfa to the phot ap ed e iec e i suc man e rtha a sha pw a ea isicreatez ou d each o th pian -rel ef urfaces to be photogr p d nd p ov ded fu erthat' h p oto iap icim s i produ edib liehtiwhi hi tov om e n di use y r flex: om tha surface. Th obtaini Q 'nh, Q-

raph c ima es by. th s ro ed r quirej the us of spe iall rdesi ned, althoug ot UIIIEGQSQR'.

ably complicated, light sources andmayalsoin:

vol ve certain preliminary treatmentof thefihrr faces to be photo p ed, as w l herei after appear. 7

Certain illustrative types of illuminating appaatus and pho o raphic q i ment particul l desienedi nract c ne therr ess.orthe p esen vent on are illust ate in the accom anying drawings, wherein: Y

Figure 1 is a perspective view of ,a photo,-

ns av ne ca e a, opy ho rd, and lightrsour e suitablet'foruse in photographing printing forms;

ndi eilike in accordance ,with-th t n e tio Fi u ,2 s is ann a ed; d .e vationa v ew.. parti lyin eciiqn, 0f th ap ar tii illn rat in Figure 1 F re 3 an i ar sn s i l n lan lan ation il ustratin theman in hich time.

characters or other plano -relief surfaces are illuin e du in vthe,p c e,. t e-meihodomh p e nvent on;

Figure 5 is a 7 front elevational ,view, of 1 the light- 7 ou c compri in i a par o th a para u ril ust at i ,m enompletel n suresl and "Figure '6 ;is view showing another ,t'yp, light I source which may, be ,used in practicing the in-v nt o and F u 7 i a d a rammati view llus ra in further modified light-source and camera ,;ar-, rangement in accordance with the invention.

The a hi p ratu ii i i a ed'in Figures-l and Zincludesa camera I l', a cgpiyb'gard L3,

and a source ofi-lluminationli; The, camera ,1]

may bega conventional photoengraverfsicamera;,

and is d l o ith dr p d-bed. nensil i r trated. The camera ll; is mounted uponsprings l1 orothervibration dampening rneans, and it is,

equipped with a lens l 9 of the usual type, w may include Vasconventional shutter and ariurrs diaphragm. 'Thelens .19 issupported. upon-.the

forward bellows-support 21, and that support is desirably movable'toward and away from the rear bellows-support 23 in order to permit focusing of The rear j material in the plane of the ground-glass during the photographing operation. The copy board [3 is supported at the forward end of the camera bed, and the plane of the copy board I3 is located symmetrical with, and at right angles to, the optical axis of the lens H), which is indicated by the dot and dash line 21.

The illuminating means or light-source l5 for the printing surface, printing form, or other material to be photographed is of special design. In order to accomplish the objective of a shadow area surrounding each of the plano-relief surfaces to be photographed, the'light-source must be of such dimensions, and so positioned, that light, in the form of an image of at least a portion of the light-source, Will be reflected from all parts of a plane surface coincident with the surface to be photographed to, or approximately to, the optical center of a lens symmetrically positioned in front of that surface. This means that an ideal light-source, as above described, should produce illumination equivalent to the illumination produced by a solid sheet of light having overall dimensions which are (for full size photographic reproduction) twice the corresponding dimensions of the surface to be photographed, the sheet of light being located in a plane which is parallel to the surface to be photographed and which intersects the optical axis of the lens at, or approximately at, the optical center thereof, and the intensity of the sheet of light being such that uniform density images are produced from all of the reflecting areas.

' It can be shown that in order to obtain exactly uniform density photographic images when using a light source as above described, the intensityof the illumination provided by the light-source should vary at different points in the plane of the surface being photographed as the reciprocal of the fourth power of the cosine of the angle that each such point makes with the optical axis of the camera lens. For relatively small lens angles, illumination at an intensity level corresponding to the inverse square law (i. e. even intensity illumination over the entire surface being photographed) will approximate this requirement. However, when the lens angle becomes much greater than about degrees, increased intensity illumination in the outer regions of the surface being photographed in accordance with the reciprocal of the fourth power of the cosine, as above described, will be found highly desirable. The criticality of the increase in illumination req'uired in the outer regions of the light-source depends to some extent upon the latitude of the photographic materials employed, as might be expected.

The above-stated requirements of an ideal light-source are not wholly attainable in practice. Of necessity, there must be an opening in the center of the light-source for the lens. Also, a solid sheet of light of sufficient dimensions for the illumination of the relatively large surfaces included in a printing form or the like, is not'obtainable. Thus, the light-sources actually available for use in the commercial practice of the in-? vention can constitute only approximate equivalents of'the solid-sheetlight-source, as above described: Close approximations are; however,

possible. For examplefor the illumination of relatively small area surfaces, where inversesquare law illumination is adequate, a recipro- 1 posure is not considered good practice. Another,

and more satisfactory, very close equivalent is a revolving bank of individual lamps, as illustrated at it in the drawings. This arrangement is particularly suitable for photographing complete printing forms'and similar large areas, in that it provides an easy and inexpensive means for obgestedlight-sources provide relative movement of the source of illumination and the material being photographed during the photographing operation. This is an important feature in obtaining even illumination of printing forms and other material of substantial area with an absence of spot reflections, when using practical equivalents of the ideal light-sourc described in the foregoing.

The dot and dash lines 29 in Figure 2 represent the path of a ray of light from the outer edge of the illuminating means shown in Figures 1 and 2 to the outer edge of a plane reflecting surfacedisposed on the copyboard l3, and from that surface to the optical center of the lens i9. Figures 3 and 4, wherein the lines 30 indicate the path of incident and reflected light rays, illustrate the manner in which illumination of this type produces the desired shadow area outlining the various plano surfaces contained in the type form or other material disposed on the copyboard. From an examination of Figure 3, it will be evident that almost no light will be reflected to the lens from surfaces which are not at least nearly parallel to the plane of the copyboard. It will be evident, therefore, that the light-source will produce the desired shadow area about the type, type-slugs or the other printing surfaces usually contained'in a printing form. As is well-known,

all of such surfaces are conventionally outlined by rather steep-sided, plane or curved surfaces.

The small area adjacent the optical axis of the lens which is not illuminated in exact accord with the foregoing, does not cause any difficulty, apparently because ordinary variations in the surfaces to be photographed produce a self-compensating effect.

The obtaining of illumination which will provide the outliningshadow areas and which will reflect light from the plano surfaces, as described, requires the use of a light-source which is of substantially greater area than the area of the printing surface, printing form, or othervmaterial to be'photographed, although, as will be apparent from the geometry of Figure 2, the area of the light-source may vary, depending upon the distance between the source of illumination and the material being photographed. The essential feature is that the relative dimensions and position of the light-source shall be such that the illumination produced on the surface to be photographed is equivalent to the illumination produced, during ordinary full size photography, by

' a solid sheet of light of proper intensity having overall: dim nsions which are. twice; the. CQHE:

spending dimensions; of: the sur ac torbeph toe raphed, whenvthat sheet-of light is positioned in.

a ,lplanel which. is parallel. to, the surface, to, be;

photographed and v which. intersects; the, optical. axis: of the. lens, at, or. approximately. at, theopticalv center Y thereof; Underlthe. stated condition: of ordinary, full. sizerphotography, the sheet ofilightandthe lens are, of. course, spaced from the surfaceto bephotographed a. distanceequal totwice theifocal lengthof thelens;

The most satisfactory, position for the light-l source is the abovedescribed position adjacent:

the camera 1ens, but as above noted, other arrangementsare possible, providedthat the equivalentillumination is produced. For a given focal length lens, it can be shown that if: the lightsource 'is-located nearerthe surface to be photographed; the overall dimensions and area may;-

camera or with the'1ens. It is also not essential mamas light-source be disposedin-a plane (i. e.- th at the light sou'rce be flat) although the-plane construction is greatly tobe preferred both from the viewpoint of obtaining better control of theillun in'ation, and from the viewpoint of simplifyingthe constructionand operation of the apparatus; "In view of the advantages of using a h rce ch s iib nt a l lana n which is located adjacent the lensythe lightsource illustratedfat l inEigure 2 is of the planar typeandiis shown inth'is position.

Inthefparticular ap aratusillustrated in Figure s' l and'2,the light-source IS inoludesa rotatableQli ght-support 31, which may constitute a circulardisc of plywood, or equivalent structure, having mounted thereon a pluralityof ordinary, incandescent filament, light bulbs 33, as illustrated. The light-support a1, is attached to a na "e 315 (Figure 2) which constitutes a part of a lcylindr ical hub 3l, andthe hub 31' is adapted to be disposed upon ahollowbearing member 39, so' as to permit rotation of the light-source. The bearing member 39, is illustrated as being attached totheforward bellows-support element}! of the camera, but it may desirably be attached to a separate support, to, eliminate vibration. The

lightsupport 3|, andthe hub 31 are retained.

in position on the bearinglmember 39 by asuitable retainer ring 4| andthe arrangement is such thatthe entire structure is freely rotatableon the bearing member 39. Electrical power is conducted, to thelight bulbs 33 by means of a pair of slip'rings,4 3,mounted on the forward bellows support 2!, anda brush structure 45 which is carried by the rotatable light-source itself;

'As previously noted, it is.,,intended that the lightsource l5 shal1 be rotated during the normal operation of the apparatus, and'this is accomplishedlin theillustr'ated structure by means of a combination-motor and speed; control unit 41', which is operatively connected to the rotatable lig tupports: by a V-belt49 and pulley 5|, The edge of the light-support disc is grooved to receiveth'e v belt. The individual light bulbs 33; which desirably are of the same wattage and light outl li are'soarranged'on the disc support- 3l ,-'-"tha t a 'substantially increased amountor illumination is provided in a direction outwardly from the optical axis of the camera lens.

More pe fically, the: individual lightzbulbs e3 ares-po iti ned at spaced intervalsalonga spiral;- (merely;- as, a, convenient means, of; mechanical:-

arrangement), this spiral: being indicated: by the dotand; dash line55i infigurex 5 The exact posi tion. of; each lightunitz. 33; is; however, in accords ance, with a predeterminedradial relationship to the optical axis, Thisposition is-determined by firstifixing theradial distances of the inside andioutsideilampsiinaccordance with the maxi mum. size. of the co'py to be reproduced) and then locating the additional lamps'between thesetwo limits. on such radial spacing that the radial disraphic image o f 'substantially even, intensity;

throughout the entire area thereof:

Thefa 'rrangementand spacing of the lam c also; be; determined empirically, as for example by placing a. first; surface mirror'on the, (wi yboard; then c n a s n le, p'atjdifier si radial distanceson the lamp support, and actu. ally measuring theintensity of theillumination, obtained for each lamp position, Additional; lamps can then be arranged on the lamp support,

. sofas to increase the illumination on thecbpyg bo'ardin the exactratio necessary to obtairjilev ,n,

tone images during the, photographingjopera on;

The" rotatingflightp-sourrie, [5, in, effect, scans the printing surface, printing form, orothercopy to bephotographe so asto producethe desired.

shadow area outlining the various, individual. plano relief surfaces contained therein, andfh y virtue ofthe controlledvariation inthe intensity of the illumination, it overcomes the diflicultiesv experienced, with prior 1 art illuminating means,

andparticu1arly the difiiculties rcsultingffro'm, uneven density inthe photographic images. The motion ofjthegindivdual light units, 33' also ,pree. vents localized; high intensity reflections, which,

mightimpairtheiquality ofthe. imageginthe photographic plate or transparency,

When, the, apparatus illustrated in. Figures, 1,, and. 2 is used for photographing a printing sure, face, printing form, or, thelike, themateriall to, be 'photographed is positioned. on thLcdpY, boardjso as to becentrallylocatedwith' respect, to the optical axis Z'Iof the camera lens, The. light-source I5 is thenplaced-in'operation, and; after focusing ofr the camera, II, ifnecessary, an exposure is made, in conventionalfmannen' Normally, the print or transparencywill-be the: same size as the material to be photographed, whichwill result inthe copy being locatednatag distance from the optical center of the;,-lens, I 9,; which is approximately twice the focal-length; of-nthat lens, ThQgIQUHdIgI-QSSJ5; during focus ing, and; the sensitized 5 material during the ex-,: posure,-. will be located the same :di-stance-xatwthei rearviof-the optical center ofthe lens,

halfeto one minutelwill gbe. required; In; aware; 1

ticulai'lysatisfactory embodiment of'the' apparatus. wherein standard 100 watt bulbs were used in the rotating light-source .l5, and the exposure time was within the rangeof about 40- to 60 seconds, the supporting disc 3| for the individual light bulbs 33 was rotated at a speed within the range of from about 25 to 30 R. P. M. This lightsource, had an effective diameter of about 36 inches; the lens [9 having a focal length of 18 inches, and it was found possible to accomplish satisfactory illumination of material which could be contained within acircle approximately 18 inches in diameter. Under these conditions, light reflected from substantiallyall points in a plane surface disposed in the plane of the printing surface or other material to be photographed,

and parallel to that surface, will intersect the optical axis of the lens at, or forwardly --of, the

optical center of that lens. Also, the individual plano surfaces are outlined by a shadow area, and the desired illumination is thus effected.

It will be understood, as previously noted, that it is'possible to use light-sources of other 'types,

and it is also possible to use other optical arrangements during the photographingoperation. For example, in Figure 6, there is, shown a generally fiat, light-source 59, which comprises a plurality. of fluorescent-tube units 6!, symmetrically disposed on a plane support 63. At the central portion of the light-source 59, an elongatedopening 65 is provided for the camera lens [5 with which the source of illumination is used, and it is intended that the light-source 59 shall be oscillated back and forth during the photoapparatus similar to that illustrated in Figures,

1 and 2, the light-source is desirably positioned in a plane which is adjacent the camera lens, and which is parallel to the surface to be photographed. To obtain the desired illumination in such a set-up, the maximum dimensions and the area'of the material to .be photographed should,

not be greater than one-half the maximum dimensions and the area of the light-source, as

indicated by the dotted outline 6'! in Figure ,6,

andthe material to be photographed should be located on the copyboard in a central position with respect to the optical axis of the lens. The intensity of the illumination produced on the material to be photographed by the light-source 59 is not as great as in the previously described embodiment, although quite satisfactory results can be obtained with a light-source of this character, particularly when the material to be re'-' produced is in the form of ordinary type or type slugs The illumination produced by a lightsource of this character is substantially in accordance with the inverse square law, and hence, is most suitable for use in photographing relatively small areas. 7

It is also possible to arrange the optical system in a right angle set-up, as illustrated in Figure 7. In this arrangement, the material to be copied, which is indicated at 69 and which may be a printing surface, or a combination of such surmination', indicated generally at-13, 'v'vhich" be similar to the light-source shown-in Figure 1; orFigureG, is disposed above the mirror H and the material to be photographed, and the surface of that material is illuminated by lightwhich passes through the transparent mirror. Here again; the dimensions of the light-source are. such "thata planes surface disposed in the plane: of the printing surface or other material "to be.

reproduced,.and parallel to that surface will reflect light into themirror H at such angles.

that it will intersect the optical axis of the system at, or forwardly of, the optical center of the; lens. 'The lens is indicated diagrammatically at" 15 and the photographic plate or .other sensitized material at 11. The right'angle arrangement shownin Figure '7 produces a lateral reversal of the image, as compared with theimage produced by a straight-line arrangement, such as illustrated in Figures 1 and 2, and this may be desirable for certain types of photo-mechanical reproduction. The practice of the method illustrated in Figure '7 is limited by the size of the transparent mirror II and by the cost of creating, F

as is done in a microscope. This is quite satis factoryfor small areas, but is somewhat inefiicient for large areas,'probably .due tolfthe scattering of light on both sides of the mirror. v

In the interest of using as small a light-source as possible, the maximum dimensions of that. source need be no greater than is necessarytoj cause light reflected from "a plane surface dis.

posed at the edge of, and parallel. to, thematerial to be. photographed to intersect the optical axis of the lens at the optical centerof that lens. Preferably, the light-source is flat, asin the illustrated embodiments, and is disposed in a plane which is parallel to, the surface of the material which is to be photographed. The light-source. may be positioned at various points along the optical axis of the system, but as previously explained, it is most desirably positioned adjacent the. lens. Itwill also be understood that the light-source need not be planar, although from a constructional viewpoint, this ar rangement is greatly to be' preferred.

In addition to the provision of a light-source] which creates a. shadow area outlining the'individual plano-relief printingsurfaces to be photo; graphed, the "accomplishment of allof the ad? vantages of the method of the present invention requires-that the surfaces to be photographed shall be abraded so as to produce a non-direcfaces as in a printing form, is positioned in a tional, uniform, matte surface thereon, prior to.

the photographing operation. Also, in orderto accomplish all of the advantages of. the invention, it will usually be found necessary-to treat,

the background surfaces of the copy material so as to suppress light reflection from those surfaces. Light-sources, asabove described, provide an outlining shadow area around-the -individual printing surfaces, but because the backgroundsurfaces are normally curved or ofvary ing angular relation with reference to the plane of the light sourceland may be parallel'to that" plane, in certa-in.regions;-as illustrated for ex-1;

ample at .19 in .Figures 3 and 4) light will be refiected from these regions into the lens, unless such reflection is suppressed.

Reflection from the background surfaces can be conveniently suppressed by applying a lightabsorbing coating to those surfaces, as for example, in accordance with the procedur set forth in my prior'application, S. N. 20,214. As therein described, the coating may comprise a mixture of Water, liquid soap, and a light-absorbing pigment, which is sprayed onto the entire area of the surface to be photographed and is subsequently removed from the printing surfaces only by the use of a cloth-covered block or felt or equivalent means. Other coatings, such as optical lacquer and the like, may also be used, but a water soluble coating is preferred because it is very easy to remove after use.

The abrading of the surface to produce a uniform matte finish may also be accomplished, in accordance with the general procedure set forth in my prior applications. N. 20,214. As described in that application, very satisfactory results can be obtained when the abrading is accomplished by the use ofa block of rubber or rubber-like compound containing fine abrasive material, similar to' the metal polishing blocks in common use in the jewelry and metal-polishing industries. In the practice of the method of the present invention, however, it is quite important that the matte surface shall be non-directional in nature. In other words, the lines should be -produced by rubbing the block or other abrasion-carrying material, over the surface in a plurality of different directions. Also, the individual lines produced by the abrasion operation should "be sufficiently small to be incapable of resolution in the optical system of the camera. In ordinary, full-scale photographic reproduction processes, this means that the individual lines should not have a greater width than about one thousandth of an inch, and preferably should not have a greater width than about one ten-thousandth of an inch.

When the material to be photographed contains etched copper or zinc plates, which frequently have the original photo-resist still in place thereon, the abrasion is best accomplished by the use of fine, abrasive dust, such as very "fine'pumice, flower of emery, diatomaceous earth,

or similar abrasive material, which will remove the resist as well as abrade the printing surfaces. Abrasive materials of this type are conveniently applied to the surface of the-plate by means of a moistened pad of-cotton or cloth. A fine grade of kitchen cleaner can sometimes be used for this purpose. Since these materials are frequently light in color, the abrasion of resistbearing copper and zinc plates is most advantageously accomplished prior to the application of the background coating of light absorbing material. Here again, the application should be non-directional in character.

The surface resulting from the abrasion pro- *cedure described above has a substantially uniform, non-directional, matte "finish, which acts to reflect a high percentage .of incident light in accordance with the cosine law, but which, at

the same time, produces sufilcient diffusion of the reflected light to produce what is generally designated in the illumination art as spread re- This :tends to even out irregularities in the reflecting surface and produces a much more satisfactory photographic image than is possible under conditions where true specular reflection occurs. The abrasion of the printing surfaces, as above described, does not in any way impair the printing characteristics of surfaces on which it is used, or otherwise prevent the subsequent use of such surfaces in ordinary printing operations. l

Upon the completion of the abrasion operation and the coating of the background areas'intelmediate the plane-relief surfaces to bephotographed with a suitable light absorbing coating, the printing form or other copy materialto be reproduced is ready for photographing. Because of the arrangement of the light-source which produces a shadow area completely outlining each of the individual surfaces to be reproduced, particularly sharp photographic images of those surfaces can be obtained, even when the printing form or other copy contains printing surfaces made of differing metals. In instances where surfaces of difiering metals are to be photographed simultaneously, it is particularly important that the abrasion of the surfaces to be photographed shall be non-directional in nature and that all background surfaces extending between the shadow area produced by the light-source shall be treated to suppress light reflection therefrom; it is also quite important that the light-source shall move relative to the surface being photographed during the photographing operation. This eliminates spot reflections, and to a large extent, compensates for any inequalities in the light output of the component parts of the lightsource.

One of the most important advantages of the present invention results from the fact that a printing form can be photographed without requiring a make-ready operation, make-ready being the operation followed in evening the height of the various elements in a printing form. The usual printing forms always include at least some elements which are of different height than the other elements in the form, and these must be leveled in ordinary printing in order to obtain a satisfactory ink print. Due to the high intensityof illumination which is made possible by the present invention, it is possible, without unduly increasing the exposure time, to stop-down the lens sufficiently to provide a depth of field which will include all of the constituent elements of the printing form, despite variation-in the height of those elements.

The practicing of the invention, when using conventional photographic material, results in a positive image which can be produced on sensitized paper for pasting up with other copy and re-photographing, or a positive film'can 'be made for use directly on a press plate. Contact'neg'atives can be made from the film positive, or the film positive can be reversed chemically, depending on the process to be followed. Also, lateral reversal of the image can be obtained by the use of straight-line image-reversers, a mirror behind the lens, or .the recently developed direct reing it over.

versing films which can be exposed from either side, or by using thin-base film and then turn- Strip film turned over can also-be used in obtaining a reversed image, or a contact negativemade from the positive can be reversed chemically to yield a reverse readingpositi've Other variations and arrangements in the use of the apparatusandprocedure of theinventi'on will suggest'themselves to those skilledjinjthe art. JIhe most ,importantadvantage of the invention results from the ability of the apparatus and procedure to make possible the direct photographing of printing forms and copy material containing spaced-apart, plano-relief printing surfaces of small area, by the use of conventional photographic materials and procedures, so as to obtain a high contrast, uniform density print or transparency which can be used in the photoinechanical art. Various of the features of the invention believed to be new are expressly set forth in the appended claims.

I claim:

1. The method of photographing printing forms and like copy material containing spacedapart, plano-relief printing surfaces, which comprises treating the background of said copy material to suppress light reflections from the nonvprinting areas of said copy material, abrading said printing surface to produce thereon a uniform, non-directional, matte finish, illuminating said copy material by a planar light source which has over-all dimensions that are at least twice the corresponding dimensions of the copy material to be photographed, which is located ad- ,jacent the lens in a plane that is normal to the optical axis of the lens and which is of increasing intensity in a direction outwardly from -maximum width of the abrasion lines is within the range of from about .001 to .0001 inch, illuminating said copy material by a planar light ,source which has over-all dimensions that are -at least twice the corresponding dimensions of the copy material to be photographed, which is located adjacent the lens in a plane that is normal to the optical axis of the lens and which is of increasing intensity in a direction outwardly from the said optical axis such that the light intensity at any point on the surface of the copy material to be photographed varies in accordance with the reciprocal of the fourth power of the cosine of the angle which such point makes at the optical axis of the lens, and then photographing said copy material.

3. The method of photographing a printing element containing metallic relief printing surfaces, which comprises applying a light-absorbing coating to the entire surface of said element, j removing said coating from said relief printing surfaces while leaving the coating intact on the background portions of said printing element, abrasively treating said printing surface to pro- V duce thereon a clean, matte finish of such fineness that the individual lines in said surface are not visible to the naked eye, illuminatingsaid printing element by a generally planar light source which has overall dimensions that are at least twice the corresponding dimensionof the material being photographed, which is located adjacent the lens in a plane that is substantially normal to the optical axis of the lens and which is of increasing intensity in a direction outwardly from the optical axis of the lens such that the 'acoaaes light intensity at any point on the surface of the material to be photographed by a planar light source which has overall dimensions that are at least twice the corresponding dimensions of the copy material to be photographed, which is located adjacent the lens in a plane that is normal to the optical axis of the lens and which is of increasing intensity in a direction outwardly from the optical axis such that the light intensity at any point in the surface of the copy material to be photographed varies in accordance with the reciprocal of the fourth power of the cosine of the angle which such point makes with the optical axis of the lens, and photographing said copy material.

5. The method of photographing printing forms and like copy material containing spacedapart, plano-relief printing surfaces and a light absorbing background, which comprises abrading said printing surfaces to produce thereon a uniform, non-directional matte finish, illuminating the material to be photographed by the use of a generally planar light source which is centered about the lens of the camera in a plane substantially normal to the optical axis of the lens, said light source having over-all dimensions which are at least twice the corresponding dimensions of the copy material to be photographed, and said light source being of increasing intensity in a direction outwardly from the optical axis of the lens, such that the intensity of the illumination at different points on the surface of the copy material varies approximately as the reciprocal of the fourth power of the cosine of the angle that each such point makes at the optical axis of the lens, and then photographing said copy material.

GEORGE L. MORRISON.

REFERENCES CITED UNITED STATES PATENTS the Number Name Date 1,033,404 Huebner July 23, 1912 1,559,710 Kunz Nov. 3, 1925 1,669,821 Grass May 15, 1928 1,928,181 Loening Sept. 26, 1934 2,346,490 Huebner Apr. 11, 1944 2,456,608 Alger Dec. 21, 1948 FOREIGN PATENTS Number Country Date 401,511 Great Britain Nov. 16, 1933 616,367 Germany 1 July 26, 1935 OTHER REFERENCES Clerc, "Ilford Manual of Process Work, Ilford Ltd, London, 1946, page 244. 

1. THE METHOD OF PHOTOGRAPHING PRINTING FORMS AND LIKE COPY MATERIAL CONTAINING SPACEDAPART, PLANO-RELIEF PRINTING SURFACES, WHICH COMPRISES TREATING THE BACKGROUND OF SAID COPY MATERIAL TO SUPPRESS LIGHT REFLECTIONS FROM THE NONPRINTING AREAS OF SAID COPY MATERIAL, ABRADING SAID PRINTING SURFACE TO PRODUCE THEREON A UNIFORM, NON-DIRECTIONAL, MATTE FINISH, ILLUMINATING SAID COPY MATERIAL BY A PLANAR LIGHT SOURCE WHICH HAS OVER-ALL DIMENSIONS THAT ARE AT LEAST TWICE THE CORRESPONDING DIMENSIONS OF THE COPY MATERIAL, TO BE PHOTOGRAPHED, WHICH IS LOCATED ADJACENT THE LENS OF THE LENS SUCH THAT THE LIGHT OPTICAL AXIS OF THE LENS AND WHICH IS OF INCREASING INTENSITY IN A DIRECTION OUTWARDLY FROM THE OPTICAL AXIS OF THE LENS SUCH THAT THE LIGHT INTENSITY AT ANY POINT ON THE SURFACE OF THE COPY MATERIAL TO BE PHOTOGRAPHED VARIES SUBSTANTIALLY IN ACCORDANCE WITH THE RECIPROCAL OF THE FOURTH POWER OF THE COSINE OF THE ANGLE WHICH SUCH POINT MAKES WITH THE OPTICAL AXIS OF THE LENS, AND THEN PHOTOGRAPHING SAID COPY MATERIAL. 